J. ELECTROCARDIOLOGY, 7 (2) 183-185, 1974

A Rare Form of Wenckebach Atrioventricular Block BY WILLIAM S. ABERNATHY, M.D.

SUMMARY A pat ient with an acute inferior trans-

mural myocardial infarction demonstrated a rare form of Wenckebach atrioventricular block, characterized by increasing P-R inter- vals, constant P-R increments, and constant R-R intervals, leading to a non-conducted beat. Constant P-R increments (the change between successive P-R intervals) have not been previously described in Wenekebach atrioventricular block.

Wenckebach atr ioventr icular (AV) block typically shows progressively increasing P-R intervals , decreasing P-R increments (the change between successive P-R intervals), and decreasing R-R intervals leading to a non-conducted beat which terminates a cycle. Several atypical forms have been reported. The patient presented here had a rare form of Wenckebach AV block characterized by a -constant P-R increment resulting in a con- s tant R-R interval.

CASE REPORT L. J. (UMMC #1242-516), a 46-year-old

man, was admitted to the hospital with an- gina pectoris of 2 hrs dura t ion. Physical examination was normal except for a third heart sound on auscultation. Within 3 days of admission the electrocardiogram showed an evolving acute infer ior t r a n s m u r a l myo- cardial infarct ion. The QRS dura t ion in- creased from an initial value of 0.10 sec to 0.12 sec. Sequential determinations of serum gtutamic oxalacetic t ransaminase, creatine phosphok inase , and lactic acid dehydro- genase were cons i s t en t w i th an acute myocardial infarction.

Reprint requests to: William S. Abernathy, M.D., Section of Cardiology (Heart Station), The Uni- versity of Michigan Medical Center, Ann Arbor, Michigan 48104.

183

Forty-two hours after admission Wenck- ebach AV block was present (Fig. 1-3). His only medications at this time were diazepam (Valium) 5 mg orally every 6 hrs and dioctyl sodium sulfosuccinate (Colace) 100 mg orally every 12 hrs. A temporary demand pace- m a k e r was i n se r t ed and u t i l i zed in ter - mit tent ly for 3 days after which time normal AV conduction resumed. Three months later, the P-R interval was 0.14 sec, and the QRS duration was 0.12 sec with a right bundle branch block pattern.

DISCUSSION Wenckebach AV block and its a typical

forms have been reviewed. I s Four forms have been described: (1) Classically, the P-R inter- vals progressively increase, the P-R incre- ments decrease, and the R-R intervals de- crease (Fig. 1, 3rd cycle). (2) The P-R incre- ment may suddenly or gradually increase be- fore the dropped beat producing an unex- pectedly long R-R i n t e r v a P '~ (Fig. 1, 1st cycle). (3) The P-R interval may suddenly de- crease before the non-conducted beat leading to an unexpected shortening of the R-R inter- val. This has been attributed to conduction in the supernormal period. 7's (4) The P-R inter- vals may vary randomly in the cycle. In this case the dropped beat does not always follow the beat with the longest P-R interval, but the first beat of each cycle always has the shortest P-R interval2

The case presented here is unique because some of the Wenckebach cycles show a con- s tant increment of change in successive P-R intervals (Fig. 1, 2nd cycle; Fig. 2, 3rd cycle; Fig. 3). To the author's knowledge this form of Wenckebach AV block has not been described before. The fundamental feature is not the constant R-R interval, since tha t may be pro- duced by a changing atrial rate (Fig. 2, 1st cycle). The constant P-R increment is the uni- que feature.

Knowledge of these a typ i ca l forms of Wenckebach AV block wil l aid in the interpretation of some complex rhythms, al- t h o u g h the c l inical and physiologic significance of these patterns is not known.

184 A B E R N A T H Y

A

A-V

L i i ~ ! i

i ii ?i:

L ~: - 2

F . ' : " ~rz

V

~ ~ ! : 1 ; ; : ; . ~ t ; ! ' . : ~ . ' ~ ! . : : : : : ; ' . ; : : F , " : ; L ~ ' L ~ ~ -

I , , ~ ~ -~ z t . . . . ~ . ~ . . . . . . . . . ~ I ~ i i I I ' : ~ ~

A-V

V

-4

I - - - - 4 - - -

+ _

i _ t - f

t ~

A-V

Figs. 1-3. Trans-sternal lead electrocardiogram recorded at 25 mm/sec on paper marked for 50 mm/sec reading. Time lines 0.08 sec apart, Values for P-P, P-R, and R-R intervals are shown to the nearest 0.01 sec in the lines marked A, A-V, and V. See text for discussion.

J. ELECTROCARDIOLOGY, VOL. 7, NO. 2, 1974

WENCKEBACH AV BLOCK 185

R E F E R E N C E S

1. DRESSLER, W, AND SWILLER, S L: Atypical Wenckebach periods with dropped atrial beats. Am J Cardiol 2:575, 1958

2. CASTILLO C, MAYTIN, O, AND CASTELLANOS, A: His bundle recordings in atypical a-v nodal Wenckebach block during cardiac pacing. Am J Cardiol 27:570, 1971

3. DREIFUS, L S, WATANABE, Y, HAIAT, R, AND KIMBIRIS, D: Atrioventricular block. Am J Car- diol 28:371, 1971

4. BELLET, S: Clinical Disorders of the Heart Beat. Second Ed. Lea & Febiger, Philadelphia, 1963, pp 328-331

5. MYERBURG, R J, GOODMAN, J S, AND MARRIOTT, H J L: Atypical forms of the Wenckebach phe- nomenon. Am J Cardiol 11:418, 1963

6. DAMATO, A N, GALLAGHER, J J, SCHNITZLER, R N, AND LAU, S H: Use of His bundle recordings in understanding a-v conduction disturbances. Bull N Y Acad Med 47:905, 1971

7. SCHERF, D, AND SCHOTT, A: The supernormal phase of recovery in man. Am Heart J 17:357, 1939

8. MACK, I, LANGENDORF, R, AND KATZ, L N: The supernormal phase of recovery of conduction in the human heart. Am Heart J 34:374, 1947

9. CHESLER, E, AND SCHAMROTH, L: The Wenck- ebach phenomenon associated with sialorrhea. Br Heart J 19:577, 1957

J. ELECTROCARDIOLOGY, VOL. 7, NO. 2, 1974